Retractable assemblies are widely used in analytical measurements technology. They serve for introducing and removing probes to and from a process and its media without process interruption. The probes are secured in an immersion tube and, by means of a drive, moved manually or automatically, for example, pneumatically, axially between a process position and a service position. These events happen within a certain timing cycle or as a function of other determinable or measured parameters.
Probes in the sense of this invention comprise probes with at least one accommodation for at least one sensor for measuring one or more physical or chemical, process variables.
The fields of use of retractable assemblies for measuring physical or chemical, process variables of a medium, e.g. a fluid, especially a liquid, in process technology are many. Sensors are used for determining the process variables, wherein the sensors can be, for example, pH-sensors, conductivity sensors, optical or electrochemical sensors for determining a concentration of a substance contained in the medium to be monitored, e.g. O2, CO2, certain types of ions, organic compounds, etc.
If retractable assemblies are used for accommodating a sensor for determining at least one process variable, the sensor can be checked, calibrated, cleaned and/or replaced in the service position, wherein the sensor is located, in such case, in a treatment chamber arranged in the housing of the retractable assembly.
Retractable assemblies are available from the group of firms, Endress+Hauser, in a large multiplicity of variants, one example being that bearing the designation, “Cleanfit H CPA475”.
Frequently, high temperatures and, especially, high pressures reign in a process. A process pressure of 10 bar and more is no rarity. If the immersion tube is in the process run-in position (process position), this pressure acts then also on the immersion tube, and the immersion tube has the tendency to be pressed back into the assembly. This must be prevented, since, otherwise—in the simplest case—the measuring can be corrupted/prevented, or—in the worst case—safety of the operating personnel or the environment can be endangered when process medium escapes without control. As long as the drive is working correctly, there is no problem. If, however, for some reason, the drive is no longer capable of functioning, the immersion tube can be pushed by the process pressure back into the assembly and therewith into an undefined position.
Equally, such reasoning holds for the opposite case, namely, when the immersion tube is located in the service position, an uncontrolled drawing of the immersion tube into the process must be prevented.
Known from the state of the art (compare the mentioned CPA475) are manually locking bolts, which lessen the degree of automation, and, in the case of improper handling, represent a significant safety risk.
European Patent EP 0545 177 A1 shows a safety system for an immersion tube, wherein its shiftability from the process position is blocked when the drive becomes non-functional. However, in the case of intact drive, the immersion tube can still be manually pushed into the process or drawn from the process. Moreover, additional lines/hoses are needed for the safety system.